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The ultrasound absorption coefficient in fresh excised rat liver has been obtained at 1-MHz fundamental frequency in the intensity range (SPTP) from low intensity (50 W cm−2) to high intensity (800 W cm−2). At atmospheric pressure the pressure absorption coefficient starts at 0.035 (50 W cm−2) and rises to 0.090 (800 W cm−2). Theoretical calculations over this same intensity range show agreement in the shape of the absorption coefficient curve as a function of intensity up to approximately 450 W cm−2. Above this intensity the experimentally derived values flatten off and slightly decline with increasing intensity. The theory shows no such characteristic. The absorption coefficient was also measured in the same intensity range at a pressure of 350 lb in.−2. (This pressure provides a bias for 193 W cm−2 at 1 MHz.) There is a small (10%) and statistically significant reduction in the absorption coefficient in the intensity range from 200–500 W cm−2 but below and above this range there is no statistically significant difference in the absorption values from those obtained at atmospheric pressure. Attenuation losses show the same characteristic charges with intensity as does the absorption coefficient but the total attenuation loss is approximately twice that due to absorption alone. [Work supported by NIH grant 5R01 CA 41073-05.]